1. Field of the Invention
This invention relates to the continuous molding of polymer elements, such as thermoplastic slide fastener elements.
2. Description of the Prior Art
The prior art contains a number of apparatus and processes for continuous molding of thermoplastic elements such as slide fastener elements on the edge of a continuous tape. U.S. Pat. No. 2,511,402 discloses such an apparatus including a drum member having cavities arranged on the periphery thereof with a noncircular annular member having cavities cooperating with the cavities in the drum member to form complete element cavities for molding elements on the edge of a tape positioned between the drum and annular member. There are a number of flexible strong metal materials, such as certain stainless steels, which can be employed for forming flexible belts or bands enclosing mold cavities in the periphery of a cavity wheel; however these bands have been limited to a maximum thickness generally about 0.001 times the diameter of the wheel since greater thicknesses heretofore have been subject to fatigue and breakage of the band after a relatively short period of use. When cavities are formed in the band, the band must have a sufficient thickness to accommodate such cavities. The formation of symmetrical slide fastener elements by molding directly on the edge of a tape requires cavities in the band of such depth, e.g. 0.15 centimeter in a band of 0.2 centimeter thickness, that a wheel with a very large diameter, e.g. two meters, would be necessitated to permit the use of a continuous molding apparatus employing a band and molding wheel; such large diameter molding wheels and consequently long bands would require a great deal of effort and expense to manufacture.